1. 12500 Onan Generator No Fuel
2. Onan Qd 12500 Fuel Filter Replacement
3. Onan Qd 12500 Service Manual

If you blink you may miss it. That may be a bad pun, but it is the truth when it comes to Onan generators. When something goes wrong, the generator will send out a code to tell you the problem. If you blink, you may miss the number of the error code.

How to Read Onan Generator Fault Codes: It’s not hard to read the Onan Fault Code blink system, once you get used to it. They use a blink and pause design to make their numbered codes clear and not confusing. For example, if the light blinks 5 times then pauses, then blinks 1 more time, that signifies Fault Code 51.

To learn more about the different Onan Fault Codes, what they mean and how to fix the problem, just keep reading our article. All the information is here for you to learn from. Onan Fault Codes are easy to learn if you do not blink while they are sending their message.

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Onan Generator Fault Code List

Code 2 - Low Oil Pressure

This code will only blink twice. It shows that the generator is low on oil and you need to add more. Twist off the yellow cap to look at the gauge and see how much more you need to put in.

Just remember to not over-fill your oil tank. Too much oil is not a good thing

Code 3 - Service Check

When you see this code, it indicates that there is a problem somewhere on your Onan generator. You will get 3 flashes then a pause, then 3 flashes, then a pause and on it goes till you press the button to get the secondary code.

The secondary code will give you the specific problem that is wrong with your generator

Code 4 - Over Crank

The first thing you need to do when you see this code is to try to reset your control board. You do this by turning the switch off and then hit the reset button. Next, you need to turn the switch back to run. If it starts you are fine. If it doesn’t and the code returns, then you need a new control board

Code 12 - Over Voltage

This problem comes from a faulty inverter and that part is overcharging the generator. The only way to solve this Fault Code problem is to take the generator to a qualified Onan dealer or repair shop.

Alternative sources for this code may be a lack of fuel or a clogged filter problem. Then you just add more fuel or replace/clean the filter

Code 13 - Under Voltage

This code tells you that the controller is incapable of maintaining proper voltage levels. There is a simple fix to this problem. Unplug all unneeded appliances while the air conditioner and battery charger are running.

Another source for this problem would be that the engine slowed down for a variety of reasons like a lack of fuel.

Code 14 - Over Frequency

This code tells you that the engine is running too fast and the sources for this code could be one of the following reasons: air leak at the intake, carb, and linkages not properly installed, misadjusted governor, broken governor.

Check your frequency levels first. Then clean or replace your carb, check to make sure the linkage is not reversed or replace the governor. For more info, read our Onan generator fault code 14 guide.

Code 15 - Under Frequency

This is the opposite of the above code. When you see this number, your engine is running too slow. The solution may be that everything was not connected properly or that the governor is in the wrong spot. It has to be in the 5^thnotch from the right.

If the generator still flashes, you may have restarted your generator in under a minute and are running in ERO mode. You get the engine running but no power in this mode. Turn the generator off and wait for at least 2 minutes before restarting.

Code 19 - Governor Actuator Overload

The governor has one wire to the controller and one wire for ground. If either one is loose, that will trigger this code. All you have to do is tighten the loose wire and you should be good to go.

If that doesn’t work or the wires are tight, the manual states that you are to go to a certified Onan repairman and get the problem looked at.

Code 23 - Low Oil Pressure Cutoff Switch

This code would indicate a problem with the cutoff switch itself. There is a malfunction in the switch and you probably won’t be able to fix it yourself.

The manual states that you need to go to the nearest certified Onan dealer to get the problem solved for you. There will be a lot of these type of solutions throughout this code explanation

Code 27 - Voltage Sense Error

What this fault code tells you is that the controller cannot sense the output voltage. Again, this problem may be beyond your expertise to repair. The manual states that the only solution is to go to your authorized Onan dealer to rectify the issue.

Code 29 - High Battery Voltage

This is the simple way to say that the voltage across your battery system is more than 19 volts. What you need to do is check your battery bank connections and if necessary, reconnect them in the proper order.

12-volt connections need to be parallel and 24-volt connections are done n a series. Another solution would be to set a lower battery boost charge rate

Code 31 – Overspeed

3 flashes, a pause and then one flash tells you that your Onan generator is going faster than 3,400 rpm. The trick here is to make sure you do not confuse 13 with 31. You can double-check by pressing the stop button 3 times in 5 seconds.

Once you return to the initial 3 flashes press the stop button again to get the secondary code to double-check your first reading. When you confirm the 31 code, you need to take the generator to the certified Onan dealer to get it fixed

Code 32 - Low Cranking Speed

This code informs you that your cranking speed is below 180 rpms for 2 seconds. To solve this problem, you need to clean the battery connections, or recharge/replace the batteries or replace the engine oil with the proper viscosity

Code 35 - Control Card Failure

During a self-test you may see this code pop up. The generator is telling itself that there is an error in the microprocessor EEPROM. You won’t be able to fix this issue and need to take it to the certified Onan dealer near you.

Code 36 - Engine Stopped

That is without command by you. You could be out of fuel or you have a low LPG pressure issue, or your spark plug leads may be loose, or you have bad spark plugs. Finally, you may have to clean or replace the air cleaner or check for some other mechanical failure.

Code 37 - Invalid Generator Set Configuration

This simple message simply says that your Onan generator is set at the wrong frequency. To correct this issue, you should see your certified Onan dealer. They have the right tools to handle this problem

Code 38 - Over Current (Field Overload)

Or in simple English, you have too many appliances running at the same time. Also, you should check your air conditioner and other appliances to make sure there is not a problem with them.

Code 41 - Generator Rotor

Your controller is not sensing either field or output voltage. This is probably another issue you will not be able to fix yourself and the manual says for you to take your generator to an authorized Onan dealer for repairs.

Code 42 – Processor

This number tells you that your Onan generator detected an error within its Microprocessor Rom section. Again, you should not tackle this problem yourself but take your generator to your nearest certified Onan dealer.

Code 43- Processor Fault Code.

There is a problem with the Microprocessor RAM and see above to find the fix.

Code 45 - Speed Sense

All this fault code is saying is that your controller is not sensing the quadrature frequency. The simple fix for this issue is for you to bring your generator into the certified Onan dealer’s shop and let them fix it for you.

Code 47 – Ignition

Once again the issue lies with the controller. It is not in bad shape, but it cannot sense any ignition when you try to start your generator. This also is an issue for your certified Onan dealer to handle.

Code 48 - Generator Field Sense

Once again, the controller is unable to sense a vital part of your generator’s operating system. This time it is the field voltage that escapes its attention. See your authorized Onan dealer to fix this problem.

Code 51 – Processor

This is another key code telling you that there is a problem with the installed microprocessor. You will need to see your qualified Onan dealer to get this taken care of.

Code 52 - Fuel Injector

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Here you have an open or short circuit in your fuel injector. This is another problem the manual says you need to take to your Onan dealer to get it taken care of.

Code 54 - MAT Sender

The MAT sender has an open or short circuit in it and it may be beyond your abilities to fix yourself. The manual states to bring your generator to your trusty Onan dealer to fix.

Code 56 - MAP Sender

This is not the same as the MAT. But the problem is the same with an open or short circuit in your MAP sender. The solution is the same as your Mat solution.

Code 57 - Over Prime

When your prime mode goes past 3 minutes, then this error code will appear. Check for and then remove any object that may be keeping the control switch in the prime position

Code 58 - Exhaust Gas Temperature Shutdown

What causes this error code is a lean fuel supply, restricted exhaust system, bad ignition system, bad heat sensor, and other issues. To keep your warranty valid, you need to take your generator to your Onan dealer for diagnosis and repair.

Code 81 - Exhaust Gas Temperature Sensor Open

This may mean that your temperature sensor is stuck open and will not close. It is best if you take your generator to your local Onan dealer to have them repair the problem

Code 82 - Exhaust Gas Temperature Shorted

You have a possible short circuit and it is a problem you should not deal with yourself. Your local authorized Onan dealer has the tools and expertise to fix this issue for you

Onan Generator Code Reset

Resetting your Onan Generator is not that difficult. All you have to do is follow these simple steps and you should be fine:

• Locate the primer button. This doubles as the start and stop button on your generator
• Hold the button down for about 30 seconds- Release the button and then start your generator
• Run the generator for 15 minutes to see if the code has been cleared. If not, then you may need the help of a qualified nan repairman to fix the problem

Some Final Words

Technology does bring a lot of wonderful toys to your life. It also helps make your life a little simpler. But the one drawback to new technology is that there is always some new problem that can arise.

That is why learning and understanding fault codes is so important. Once you learn and understand them you know what you have to do to solve the problem That knowledge also makes life a little simpler to live

Onan Qd 12500 Fuel Filter Replacement

Don’t be afraid of technology, learn how to use it and learn the fault codes so you know what needs to be done next before you cause more problems that may raise your repair costs.

Onan Qd 12500 Service Manual